#include "stdio.h"
#include "stdlib.h"
#include "string.h"
#include "stdlib.h"
#include "time.h"
#include <io.h>

int 	bSwitch = 0;		// Switch == 1; No Switch == 0
int 	bAlter = 1;			// Alternate each simulation between Keep & Switch
int 	bRedir = 0;			// output redirected: 0=no, 1=yes
int 	door[3] = {0,0,0};	// The Doors (0,1,2)
int 	choice = 0;			// door initially chosen
int 	show = 0;			// door shown
int 	final = 0;			// final door after offer to switch
int 	keepitW = 0;		// # wins when keepit
int 	keepitL = 0;		// # losses when keepit
int 	switchW = 0;		// # wins when switch
int 	switchL = 0;		// # losses when switch
int 	total = 0;			// running total of simulations done
int 	keepittotal = 0;	// running total of simulations done with keepit
int 	switchtotal = 0;	// running total of simulations done with switch
int 	loop = 2000;		// # times to run simulation
int 	halfloop;			// loop/2
int 	n;					// loop countdown counter
fpos_t	pos;				// used for detecting output redirection
char *	winner;				// string identifying winning move
char	det[] = "%c %c %c %d %d %c %c ";	// used only if output redirected
char	fmt[] = "%4d, Keep: %4d=Win, %4d=Lose, Win%%=%4.1f%%.  \
Switch: %4d=Win, %4d=Lose, Win%%=%4.1f%%.  %s %d > %c";

int
getrand(int i)	// return a random number modulo i
{
	int r;

	r = rand();
	return r%i;
}

int
main(argc, argv)
int	argc;
char	*argv[];
{
	int 	i, j;		// misc counters
	float	kpc, spc;	// percents for keep and switch

	srand(time(NULL));	// set starting point for generating pseudorandom #s

	if (!_isatty(_fileno(stdout)))	// detect if stdout has been redirected
	{
		bRedir = 1;
		printf("© = car; • = goat; 1st digit = choice; 2nd digit = show; 3rd digit = switch\n"); 
	}

	// cmdline arg for help?

	if (argc > 1 && (*argv[1] == '/' || *argv[1] == '-')) // ignore / and -
		strcpy(argv[1], &argv[1][1]);

	if (argc > 1 && *argv[1] == '?')
	{
		printf("This program runs simulations of the Monty Hall Paradox,\n");
		printf("for info, see https://en.wikipedia.org/wiki/Monty_Hall_problem\n");
		printf("Half of the simulations are Keep 1st choice, half are Switch.\n");
		printf("Output is a running tally of Wins and Loses for both Keep and Switch.\n\n");

		printf("Usage: %s {a|k|s} {#simulations}\n", argv[0]);
		printf("\twhere a = alternate between keep & switch each time (default)\n");
		printf("\t      k = run all keep simulations 1st, then all switch\n");
		printf("\t      s = run all switch simulations 1st, then all keep\n");
		printf("\twhere #simulations >= 200 and <= 10 million (default=2000)\n");
		printf("\t      with half Keep original choice and half Switch choice.\n");
		printf("\tNote: { } are optional args and | means choose only one.\n\n");

		printf("Examples:\n");
		printf(" C:>montyhall         -> alternate keep & switch each of 2000 times\n");
		printf(" C:>montyhall k       -> 1000 keep followed by 1000 switch\n");
		printf(" C:>montyhall s 20000 -> 10000 switch followed by 10000 keep\n");
		printf(" C:>montyhall 2000000 -> alternate keep & switch 2 million times\n");
		printf(" C:>montyhall ?       -> print this message and exit.\n\n");

		printf("If output is redirected to a file, the file contains additional info\n");
		printf("and fewer running tallies are displayed.\n");
		printf("(However redirecting to nul produces no output at all.)\n");
		exit(0);
	}

	// cmdline arg to determine alternate or all keep 1st or all switch 1st

	if (argc > 1)
	{
		if (*argv[1] == 's')
		{
			bSwitch = 1;		// do switch fist
			bAlter = 0;
		}
		else if (*argv[1] == 'k')
		{
			bSwitch = 0;		// do keep first
			bAlter = 0;
		}
		else if (isdigit(*argv[1]))	// catch case where on # of loops given
		{
			loop = atoi(argv[1]);	// requested number of simulations to run
		}
	}
	// alternate with each simulation (default) if neither 's' or 'k' given

	// cmdline arg to set number of simulations to run (default is 2000)
	if (argc > 2 && isdigit(*argv[2]))
	{
		loop = atoi(argv[2]);	// requested number of simulations to run
	}

	halfloop = loop/2;			// needed to know when to switch keep/switch
	loop = halfloop*2;			// force even number of loops

	if (loop < 200)				// make sure # is large enough to be significant
		loop = 200;
	else if (loop > 10000000)	// prevent huge number of unnecessary loops
		loop = 10000000;


	// MAIN LOOP

	for (n=loop; n--; )	
	{
		for (i=3; --i >= 0; )	// clear all doors
			door[i] = 0;

		i = getrand(3);			// get i as door# for car
		door[i] = 1;			// set door[i] as car

		choice = getrand(3);	// choose door

		i = getrand(2);			// setup for opening a door with goat

		if (i)					// start search for goat door to show from top
		{
			for (j=3; --j >= 0; )
			{
				if (!door[j] && j != choice)	// goat & not-choice?
				{
					show = j;					//	yes = show
					break;
				}
			}
		}
		else					// search for goat door to show from bottom
		{
			for (j=-1; ++j < 3; )
			{
				if (!door[j] && j != choice)	// goat & not-choice?
				{
					show = j;					//	yes = show
					break;
				}
			}
		}

		if (!bSwitch)			// if not switching, choice is final
			final = choice;
		else					// else final is door not choice & not shown
		{
			for (j=-1; ++j < 3; )
			{
				if (j != choice && j != show)
				{
					final = j;
					break;
				}
			}
		}

		if (door[final])	// final choice door have car?
		{
			if (!bSwitch)		// yes, tally
				keepitW++;
			else
				switchW++;
		}
		else				// final choice door has goat
		{
			if (!bSwitch)		// yes, tally
				keepitL++;
			else
				switchL++;
		}

		if (bSwitch)			// increment switch total if switching
			++switchtotal;
		else					// increment keep total if not switching
			++keepittotal;
		if (++total == halfloop) // incr total & chk to switch keep/switch
			bSwitch ^= 1;		 // yes 1/2-way done, toggle switch flag
		else if (bAlter)		 // alternate each run between keep & switch?
			bSwitch ^= 1;		 // yes, then always toggle switch flag


		// print intermediate results

		if      (keepitW < switchW)  winner = "Switch";
		else if (keepitW > switchW)  winner = "Keep";
		else                         winner = "Tie";

		kpc = keepittotal ? keepitW*(float)100/keepittotal : 0;
		spc = switchtotal ? switchW*(float)100/switchtotal : 0;

		if (bRedir)	// if redirecting, print details before print running tally
		{
			char c[4];

			sprintf(c, "%d", final+1); // convert final into a char for print
			printf(det, door[0] ? '©' : '•', 
						door[1] ? '©' : '•',
						door[2] ? '©' : '•', choice+1, show+1, 
						choice != final ? c[0] : ' ',
						door[final] ? 'W' : 'L');
		}

		// print running tally

		printf(fmt, total, keepitW, keepitL, kpc, 
						   switchW, switchL, spc, 
						   winner, abs(switchW-keepitW), '\r');

		// if redirect, print current tally to stderr every 65,535 simulations

		if (bRedir && (total & 0xFFFF) == 0)
			fprintf(stderr, fmt, total, keepitW, keepitL, kpc, 
						   switchW, switchL, spc, 
						   winner, abs(switchW-keepitW), '\r');
	} // end of main loop

	// print final results

	kpc = keepitW*(float)200/total;
	spc = switchW*(float)200/total;

	printf(fmt, total, keepitW, keepitL, kpc, 
					   switchW, switchL, spc, 
					   winner, abs(switchW-keepitW), '\n');

	if (bRedir) // if redirect, print final tally to stderr
	{
		fprintf(stderr, "\rOutput was redirected. Final numbers are:                                                                             \n");
		fprintf(stderr, fmt, total, keepitW, keepitL, kpc, 
					   switchW, switchL, spc, 
					   winner, abs(switchW-keepitW), '\n');
	}
}